Molecular orientation in Langmuir-Blodgett (L-B) monolayers of poly(octadecyl methacrylate) (PODMA) and poly(octadecyl acrylate) (PODA) has been studied by infrared spectroscopy. Substantial anisotropy between the spectra measured in transmission, and by reflection at grazing incidence, was observed for both these polymers. The carbonyl group was found to be oriented approximately perpendicular to the substrate surface, independent of polymer type and of deposition surface pressure within the range investigated. The long aliphatic ester side groups were also found to be approximately perpendicular to the plane of the monolayer. However, the orientation of these groups was strongly dependent upon the chemical structure of the polymer used and on the surface pressure at transfer. More condensed L-B monolayers of PODA could be formed than was the case for PODMA, in part due to the lower steric hindrance to rotations about backbone bonds in PODA because of the absence of the methyl side group. © 1986, American Chemical Society. All rights reserved.